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      1 //==- llvm/Support/Recycler.h - Recycling Allocator --------------*- C++ -*-==//
      2 //
      3 //                     The LLVM Compiler Infrastructure
      4 //
      5 // This file is distributed under the University of Illinois Open Source
      6 // License. See LICENSE.TXT for details.
      7 //
      8 //===----------------------------------------------------------------------===//
      9 //
     10 // This file defines the Recycler class template.  See the doxygen comment for
     11 // Recycler for more details.
     12 //
     13 //===----------------------------------------------------------------------===//
     14 
     15 #ifndef LLVM_SUPPORT_RECYCLER_H
     16 #define LLVM_SUPPORT_RECYCLER_H
     17 
     18 #include "llvm/ADT/ilist.h"
     19 #include "llvm/Support/AlignOf.h"
     20 #include <cassert>
     21 
     22 namespace llvm {
     23 
     24 /// PrintRecyclingAllocatorStats - Helper for RecyclingAllocator for
     25 /// printing statistics.
     26 ///
     27 void PrintRecyclerStats(size_t Size, size_t Align, size_t FreeListSize);
     28 
     29 /// RecyclerStruct - Implementation detail for Recycler. This is a
     30 /// class that the recycler imposes on free'd memory to carve out
     31 /// next/prev pointers.
     32 struct RecyclerStruct {
     33   RecyclerStruct *Prev, *Next;
     34 };
     35 
     36 template<>
     37 struct ilist_traits<RecyclerStruct> :
     38     public ilist_default_traits<RecyclerStruct> {
     39   static RecyclerStruct *getPrev(const RecyclerStruct *t) { return t->Prev; }
     40   static RecyclerStruct *getNext(const RecyclerStruct *t) { return t->Next; }
     41   static void setPrev(RecyclerStruct *t, RecyclerStruct *p) { t->Prev = p; }
     42   static void setNext(RecyclerStruct *t, RecyclerStruct *n) { t->Next = n; }
     43 
     44   mutable RecyclerStruct Sentinel;
     45   RecyclerStruct *createSentinel() const {
     46     return &Sentinel;
     47   }
     48   static void destroySentinel(RecyclerStruct *) {}
     49 
     50   RecyclerStruct *provideInitialHead() const { return createSentinel(); }
     51   RecyclerStruct *ensureHead(RecyclerStruct*) const { return createSentinel(); }
     52   static void noteHead(RecyclerStruct*, RecyclerStruct*) {}
     53 
     54   static void deleteNode(RecyclerStruct *) {
     55     assert(0 && "Recycler's ilist_traits shouldn't see a deleteNode call!");
     56   }
     57 };
     58 
     59 /// Recycler - This class manages a linked-list of deallocated nodes
     60 /// and facilitates reusing deallocated memory in place of allocating
     61 /// new memory.
     62 ///
     63 template<class T, size_t Size = sizeof(T), size_t Align = AlignOf<T>::Alignment>
     64 class Recycler {
     65   /// FreeList - Doubly-linked list of nodes that have deleted contents and
     66   /// are not in active use.
     67   ///
     68   iplist<RecyclerStruct> FreeList;
     69 
     70 public:
     71   ~Recycler() {
     72     // If this fails, either the callee has lost track of some allocation,
     73     // or the callee isn't tracking allocations and should just call
     74     // clear() before deleting the Recycler.
     75     assert(FreeList.empty() && "Non-empty recycler deleted!");
     76   }
     77 
     78   /// clear - Release all the tracked allocations to the allocator. The
     79   /// recycler must be free of any tracked allocations before being
     80   /// deleted; calling clear is one way to ensure this.
     81   template<class AllocatorType>
     82   void clear(AllocatorType &Allocator) {
     83     while (!FreeList.empty()) {
     84       T *t = reinterpret_cast<T *>(FreeList.remove(FreeList.begin()));
     85       Allocator.Deallocate(t);
     86     }
     87   }
     88 
     89   template<class SubClass, class AllocatorType>
     90   SubClass *Allocate(AllocatorType &Allocator) {
     91     assert(sizeof(SubClass) <= Size &&
     92            "Recycler allocation size is less than object size!");
     93     assert(AlignOf<SubClass>::Alignment <= Align &&
     94            "Recycler allocation alignment is less than object alignment!");
     95     return !FreeList.empty() ?
     96            reinterpret_cast<SubClass *>(FreeList.remove(FreeList.begin())) :
     97            static_cast<SubClass *>(Allocator.Allocate(Size, Align));
     98   }
     99 
    100   template<class AllocatorType>
    101   T *Allocate(AllocatorType &Allocator) {
    102     return Allocate<T>(Allocator);
    103   }
    104 
    105   template<class SubClass, class AllocatorType>
    106   void Deallocate(AllocatorType & /*Allocator*/, SubClass* Element) {
    107     FreeList.push_front(reinterpret_cast<RecyclerStruct *>(Element));
    108   }
    109 
    110   void PrintStats() {
    111     PrintRecyclerStats(Size, Align, FreeList.size());
    112   }
    113 };
    114 
    115 }
    116 
    117 #endif
    118